1. Field of the Invention
This invention relates to a method of setting a robot coordinate system, and more particularly, to a robot coordinate system setting method which facilitates the setting of a common coordinate system shared by a plurality of robots included in a robot system and the setting of a common coordinate system with respect to a robot installed in substitution for a robot in the robot system.
2. Description of the Related Art
When globally controlling a plurality of robots included in a robot system in a factory line or the like, a robot control program described using a common coordinate system shared by all robots is usually employed. To control the operation of the individual robots, coordinate transformation matrices which relate the common coordinate system to coordinate systems uniquely set for the respective robots are used to transform commands expressed with reference to the common coordinate system into those expressed with reference to the coordinate systems related to the individual robots. To this end, coordinate transformation matrices related to the respective robots are predetermined; in other words, the common coordinate system is set with respect to each of the robots.
When setting a common coordinate system with respect to each of robots installed such that they share a common domain of motion, conventionally a jig is placed in the common domain of motion, and a known position of the jig with reference to the common coordinate system is directly taught to the individual robots so that each robot may recognize a position and orientation thereof with respect to the common coordinate system, whereby a common coordinate system is set with respect to each of the robots. Thus, to set the common coordinate system by this method, the robots must be positioned such that they share a common domain of motion. This requirement imposes heavy restrictions on the arrangement of robots and hinders suitable configuration of robot systems.
In the case of robot systems including a robot which does not share a domain of motion with the other robots thus the aforesaid method cannot be applied because it requires a jig to be positioned in the common domain of motion shared by all robots. Conventionally the setting of a common coordinate system with respect to the robots is carried out by using a special jig which all robots can access. This method is, however, disadvantageous in that a special jig must be prepared.
After the common coordinate system is once set by either of the aforementioned methods, if a robot becomes out of order and a substitute robot is installed therefor, the common coordinate system must be set with respect to this substitute robot, with a normal jig or special jig located at exactly the same position as that used before to set the common coordinate system. It is, however, difficult to place the normal or special jig at exactly the same position, and therefore, the common coordinate system must be again set with respect to each of the robots. Accordingly, restoration work of the robot system consumes labor and time.